Bottom Line:
When injected into naïve mice, PEGylated phages showed a strong increase in circulation half-life, whereas challenge of immunized mice did not reveal a significant difference.Our results suggest that the prolonged half-life is due to decreased susceptibility to innate immunity as well as avoidance of cellular defence mechanisms.PEGylated viruses elicited significantly reduced levels of T-helper type 1-associated cytokine release (IFN-γ and IL-6), in both naïve and immunized mice.

f3: Phage inactivation in the presence of innate immunity in the mouse model, both in vivo for A511 (A) and Felix‐O1 (B), and in vitro (C). In (C), 0, 1, 2 and 4 indicate the incubation time in the presence of serum. In in vivo studies, the number of phage per 5 µl at 0 h is represented as 100%, corresponded to 1 × 106 PFU for WT A511 and 1 × 105 PFU for PEGylated A511, and 1 × 106 PFU for WT Felix‐O1 and 3 × 105 PFU for PEGylated Felix‐O1. The asterisk (*) denotes statistical significance (α = 0.05).

Mentions:
The proportion of infective A511‐wt particles in the mouse blood circulation dropped rapidly; only 3.3% of the initial PFUs remained 1.5 h after injection (Fig. 3A). The decrease continued further; we measured 0.016% residual infectivity 6 h post injection, and 0.001% infective particles 24 h after injection. In contrast, PEGylated A511‐PEG phages survived much better; 83.7% and 20.9% of the PFUs remained after 1.5 and 6 h injection respectively (Fig. 3A). The A511‐PEG clearance followed an almost linear function, with 0.01% infectivity remaining after 24 h incubation (Fig. 3A). At 6 h post injection, the difference between native and PEGylated phage reached a maximum of more than 3 logs.

f3: Phage inactivation in the presence of innate immunity in the mouse model, both in vivo for A511 (A) and Felix‐O1 (B), and in vitro (C). In (C), 0, 1, 2 and 4 indicate the incubation time in the presence of serum. In in vivo studies, the number of phage per 5 µl at 0 h is represented as 100%, corresponded to 1 × 106 PFU for WT A511 and 1 × 105 PFU for PEGylated A511, and 1 × 106 PFU for WT Felix‐O1 and 3 × 105 PFU for PEGylated Felix‐O1. The asterisk (*) denotes statistical significance (α = 0.05).

Mentions:
The proportion of infective A511‐wt particles in the mouse blood circulation dropped rapidly; only 3.3% of the initial PFUs remained 1.5 h after injection (Fig. 3A). The decrease continued further; we measured 0.016% residual infectivity 6 h post injection, and 0.001% infective particles 24 h after injection. In contrast, PEGylated A511‐PEG phages survived much better; 83.7% and 20.9% of the PFUs remained after 1.5 and 6 h injection respectively (Fig. 3A). The A511‐PEG clearance followed an almost linear function, with 0.01% infectivity remaining after 24 h incubation (Fig. 3A). At 6 h post injection, the difference between native and PEGylated phage reached a maximum of more than 3 logs.

Bottom Line:
When injected into naïve mice, PEGylated phages showed a strong increase in circulation half-life, whereas challenge of immunized mice did not reveal a significant difference.Our results suggest that the prolonged half-life is due to decreased susceptibility to innate immunity as well as avoidance of cellular defence mechanisms.PEGylated viruses elicited significantly reduced levels of T-helper type 1-associated cytokine release (IFN-γ and IL-6), in both naïve and immunized mice.